The complement system comprises a set of at least 20 plasma and membrane proteins that act together in a regulated cascade system to attack extracellular forms of pathogens (Janeway et al. (1994) Immunobiology: The Immune System in Health and Disease. Current Biology Ltd, San Francisco, pp. 8:35-8:55; Morgan (1995) Crit. Rev. in Clin Lab. Sci. 32(3):265-298). There are two distinct enzymatic activation cascades, the classical and alternative pathways, and a non-enzymatic pathway known as the membrane attack pathway.
The classical pathway is usually triggered by an antibody bound to a foreign particle. It comprises several components, C1, C4, C2, C3 and C5 (listed by order in the pathway). Initiation of the classical pathway of the Complement System occurs following binding and activation of the first complement component (C1) by both immune and non-immune activators (Cooper (1985) Adv. Immunol. 37:151). C1 comprises a calcium-dependent complex of components C1q, C1r and C1s, and is activated through binding of the C1q component. C1q contains six identical subunits and each subunit comprises three chains (the A, B and C chains). Each chain has a globular head region which is connected to a collagen-like tail. Binding and activation of C1q by antigen-antibody complexes occurs through the C1q head group region. Numerous non-antibody C1q activators, including proteins, lipids and nucleic acids (Reid et al. (1993) The Natural Immune System: Humoral Factors. E. Sim, ed. IRL Press, Oxford, p. 151) bind and activate through a distinct site on the collagen-like stalk region.
Non-antibody C1q protein activators include C-reactive protein (CRP) (Jiang et al. (1991) J. Immunol. 146:2324) and serum amyloid protein (SAP) (Bristow et al. (1986) Mol. Immunol. 23:1045); these will activate C1q when aggregated by binding to phospholipid or carbohydrate, respectively. Monomeric CRP or SAP do not activate C1q. C1q is also activated through binding to aggregated β-amyloid peptide (Schultz et al. (1994) Neurosci. Lett. 175:99; Snyder et al. (1994) Exp. Neurol. 128:136), a component of plaques seen in Alzheimer's disease (Jiang et al. (1994) J. Immunol. 152:5050; Eikelenboom and Stam (1982) Acta Neuropathol (Berl) 57:239; Eikelenboom et al. (1989) Virchows Arch. [B] 56:259; Rogers et al. (1992) Proc. Natl. Acad. Sci. USA 89:10016; Dietzschold et al. (1995) J. Neurol. Sci. 130: 11). C1q activation might also exacerbate the tissue damage associated with Alzheimer's disease. These activators bind C1q on its collagen-like region, distant from the head-group region where immunoglobulin activators bind. Other proteins which bind the C1q collagen-like region include collagen (Menzel et al. (1981) Biochim. Biophys. Acta 670:265), fibronectin (Reid et al. (1984) Acta Pathol. Microbiol. Immunol. Scand. Sect. C 92 (Suppl. 284): 11), Iaminin (Bohnsack et al. (1985) Proc. Natl. Acad. Sci. USA 82:3824), fibrinogen and fibrin (Entwistle et al. (1988) Biochem. 27:507), HIV rsgp41 (Stoiber et al. (1995) Mol. Immunol. 32:371), actin (Nishioka et al. (1982) Biochem. Biophys. Res. Commun. 108:1307) and tobacco glycoprotein (Koethe et al. (1995) J. Immunol. 155:826).
C1q also binds and can be activated by anionic carbohydrates (Hughes-Jones et al. (1978) Immunology 34:459) including mucopolysaccharides (Almeda et al. (1983) J. Biol. Chem. 258:785), fucans (Blondin et al. (1994) Mol. Immunol. 31:247), proteoglycans (Silvestri et al. (1981) J. Biol. Chem. 256:7383), and by lipids including lipopolysaccharide (LPS) (Zohair et al. (1989) Biochem. J. 257:865; Stoiber et al. (1994) Eur. J. Immunol. 24:294). Both DNA (Schravendijk and Dwek (1982) Mol. Immunol. 19:1179; Rosenberg et al. (1988) J. Rheumatol 15:1091; Uwatoko et al. (1990) J. Immunol. 144:3484) and RNA (Acton et al. (1993) J. Biol. Chem. 268:3530) can also bind and potentially activate C1q. Intracellular components which activate C1q include cellular and subcellular membranes (Linder (1981) J. Immunol. 126:648; Pinckard et al. (1973) J. Immunol. 110: 1376; Storrs et al. (1981) J. Biol. Chem. 256:10924; Giclas et al. (1979) J. Immunol. 122: 146; Storrs et al. (1983) J. Immunol. 131:416), intermediate filaments (Linder et al. (1979) Nature 278:176) and actin (Nishioka et al. (1982) Biochem. Biophys. Res. Commun. 108:1307). All of these interactions would recruit the classical pathway for protection against bacterial (or viral) infection, or as a response to tissue injury (Li et al. (1994) J. Immunol. 152:2995) in the absence of antibody.
A binding site for non-antibody activators including CRP (Jiang et al. (1991) J. Immunol. 146:2324), SAP (Ying et al. (1993) J. Immunol. 150:169), β-amyloid peptide (Newman (1994) Curr. Biol. 4:462) and DNA (Jiang et al. (1992) J. Biol. Chem. 267:25597) has been localized to the amino terminus of C1q A chain at residues 14-26. A synthetic peptide comprising this sequence effectively inhibits both binding and activation. The peptide 14-26 contains several basic residues and matches one of the heparin binding motifs (Yabkowitz et al. (1989) J. Biol. Chem. 264:10888; Cardin et al. (1989) Arteriosclerosis 9:21). The peptide is also highly homologous with peptide 145-156 in collagen-tailed acetylcholinesterase; this site is associated with heparin-sulfate basement membrane binding (Deprez et al. (1995) J. Biol. Chem. 270:11043). A second C1q A chain site at residues 76-92 also might be involved in weaker binding; this site is at the junction of the globular head region and the collagen-like tail.
The second enzymatically activated cascade, known as the alternative pathway, is a rapid, antibody-independent route for the Complement System activation and amplification. The alternative pathway comprises several components, C3, Factor B, and Factor D. Activation of the alternative pathway occurs when C3b, a proteolytic cleavage form of C3, is bound to an activating surface such as a bacterium. Factor B is then bound to C3b, and cleaved by Factor D to yield the active enzyme, Ba. The enzyme Ba then cleaves more C3 to C3b, producing extensive deposition of C3b-Ba complexes on the activating surface. When a second C3b is deposited, forming a C3b-C3b-Ba complex, the enzyme can then cleave C5 and trigger activation of the terminal pathway.
The non-enzymatic terminal pathway, also known as the membrane attack pathway, comprises the components C5, C6, C7, C8 and C9. Activation of this membrane attack pathway results when the C5 component is enzymatically cleaved by either the classical or alternative pathway to yield the small C5a polypeptide (9 kDa) and the large C5b fragment (200 kDa). The C5a polypeptide binds to a 7 transmembrane G-protein coupled receptor which was originally described on leukocytes and is now known to be expressed on a variety of tissues including hepatocytes (Haviland et al. (1995) J. Immunol. 154:1861) and neurons (Gasque et al. (1997) Am. J. Pathol. 150:31). The C5a molecule is the primary chemotactic component of the human Complement System and can trigger a variety of biological responses including leukocyte chemotaxis, smooth muscle contraction, activation of intracellular signal transduction pathways, neutrophil-endothelial adhesion (Mulligan et al. (1997) J. Immunol. 158:1857), cytokine and lipid mediator release and oxidant formation. The larger C5b fragment binds sequentially to later components to form the C5b-9 membrane attack complex (MAC). The C5b-9 MAC can directly lyse erythrocytes, and in greater quantities is lytic for leukocytes and is damaging to tissues such as muscle, epithelial and endothelial cells (Stahl et al. (1997) Circ. Res. 76:575). In sublytic amounts the MAC can stimulate upregulation of adhesion molecules, intracellular calcium increase and cytokine release (Ward (1996) Am. J. Pathol. 149:1079). In addition, the C5b-9 MAC can stimulate cells such as endothelial cells and platelets without causing cell lysis. The non-lytic effects of C5a and the C5b-9 MAC are sometimes quite similar.
The Complement System has an important role in defense against bacterial and viral infection, and possibly in immune surveillance against tumors. This is demonstrated most clearly in humans who are deficient in complement components. Individuals deficient in early components (C1, C4, C2 or C3) suffer from recurrent infections, while individuals deficient in late components (C5 through C9) are susceptible to nisseria infection. Complement classical pathway is activated on bacteria by antibodies, by binding of CRP or SAP, or by direct activation through LPS. Complement alternative pathway is activated through binding of C3 to the cell coat. Complement can be activated by viruses through antibodies, and can also be activated on viral infected cells because these are recognized as foreign. In a similar way, transformed cells can be recognized as foreign and can be lysed by the Complement System or targeted for immune clearance.
Activation of the Complement System can and has been used for therapeutic purposes. Antibodies which were produced against tumor cells were then used to activate the Complement System and cause tumor rejection. Also, the Complement System is used together with polyclonal or monoclonal antibodies to eliminate unwanted lymphocytes. For example, anti-lymphocyte globulin or monoclonal anti-T-cell antibodies are used prior to organ transplantation to eliminate lymphocytes which would otherwise mediate rejection.
Although the Complement System has an important role in the maintenance of health, it has the potential to cause or contribute to disease. The Complement System has been implicated in numerous renal, rheumatological, neurological, dermatological, hematological, vascular/pulmonary, allergy, infectious, biocompatibility/shock and other diseases or conditions (Morgan (1995) Crit. Rev. in Clin Lab. Sci. 32(3):265-298; Matis and Rollins (1995) Nature Medicine 1(8):839-842). The Complement System is not necessarily the only cause of the disease state, but it may be one of several factors, each of which contributes to pathogenesis.
Several pharmaceuticals have been developed that inhibit the Complement System in vivo, however, many cause toxicity or are poor inhibitors (Morgan (1995) Crit. Rev. in Clin Lab. Sci. 32(3):265-298). Heparins, K76COOH and nafamstat mesilate have been shown to be effective in animal studies (Morgan (1995) Crit. Rev. in Clin Lab. Sci. 32(3):265-298). Recombinant forms of naturally occurring inhibitors of the Complement System have been developed or are under consideration, and these include the membrane regulatory proteins Complement Receptor 1 (CR1), Decay Accelerating Factor (DAF), Membrane Cofactor Protein (MCP) and CD59.
C5 is an attractive target for the development of a Complement System inhibitor, as both the classical and alternative pathways converge at component C5 (Matis and Rollins (1995) Nature Medicine 1(8):839-842). In addition, inhibition of C5 cleavage blocks both the C5a and the C5b effects on leukocytes and on tissue such as endothelial cells (Ward (1996) Am. J. Pathol. 149:1079); thus C5 inhibition can have therapeutic benefits in a variety of diseases and situations, including lung inflammation (Mulligan et al. (1998) J. Clin. Invest. 98:503), extracorporeal complement activation (Rinder et al. (1995) J. Clin. Invest. 96:1564) or antibody-mediated complement activation (Biesecker et al. (1989) J. Immunol. 142:2654). Matis and Rollins ((1995) Nature Medicine 1(8):839-842) have developed C5-specific monoclonal antibodies as an anti-inflammatory biopharmaceutical. Both C5a and the MAC have been implicated in acute and chronic inflammation associated with human disease, and their role in disease states has been confirmed in animal models. C5a is required for complement- and neutrophil-dependent lung vascular injury (Ward (1997) J. Lab. Clin. Med. 129:400; Mulligan et al. (1998) J. Clin. Invest. 98:503), and is associated with neutrophil and platelet activation in shock and in burn injury (Schmid et al. (1997) Shock 8:119). The MAC mediates muscle injury in acute autoimmune myasthenia gravis (Biesecker and Gomez (1989) J. Immunol. 142:2654), organ rejection in transplantation (Baldwin et al. (1995) Transplantation 59:797; Brauer et al. (1995) Transplantation 59:288; Takahashi et al. (1997) Immunol. Res. 16:273) and renal injury in autoimmune glomerulonephritis (Biesecker (1981) J. Exp. Med. 39:1779; Nangaku (1997) Kidney Int. 52:1570). Both C5a and the MAC are implicated in acute myocardial ischemia (Homeister and Lucchesi (1994) Annu. Rev. Pharmacol. Toxicol. 34:17), acute (Bednar et al. (1997) J. Neurosurg. 86:139) and chronic CNS injury (Morgan (1997) Exp. Clin. Immunogenet. 14:19), leukocyte activation during extracorporeal circulation (Sun et al. (1995) Nucleic Acids Res. 23:2909; Spycher and Nydegger (1995) Infushionsther. Transfusionsmed. 22:36) and in tissue injury associated with autoimmune diseases including arthritis and lupus (Wang et al. (1996) Immunology 93:8563). Thus, inhibiting cleavage of C5 prevents generation of two potentially damaging activities of the Complement System. Inhibiting C5a release eliminates the major Complement System chemotactic and vasoactive activity, and inhibiting C5b formation blocks assembly of the cytolytic C5b-9 MAC. Furthermore, inhibition of C5 prevents injury by the Complement System while leaving intact important Complement System defense and clearance mechanisms, such as C3 and C1q phagocytic activity, clearance of immune complexes and the innate immune response (Carrol (1998) Ann. Rev. Immunol. 16:545).
C3 is an attractive target for the development of a Complement System inhibitor, as it is common to both pathways. Inhibition of C3 using recombinant versions of a natural inhibitors (Kalli et al. (1994) Springer Semin. Immunopathol. 15:417) can prevent cell-mediated tissue injury (Mulligan et al. (1992) J. Immunol. 148:1479) and this has been shown to have therapeutic benefit in diseases such as myocardial infarction (Weisman et al. (1990) Science 249:146) and liver ischemia/reperfusion (Chavez-Cartaya et al. (1995) Transplantation 59:1047). Controlling C3 limits most biological activities of the Complement System. Most natural inhibitors, including DAF, MCP, CR1 and Factor H target C3.
SELEX™
A method for the in vitro evolution of Nucleic Acid molecules with highly specific binding to target molecules has been developed. This method, Systematic Evolution of Ligands by EXponential enrichment, termed the SELEX process, is described in U.S. patent application Ser. No. 07/536,428, filed Jun. 11, 1990, entitled “Systematic Evolution of Ligands by Exponential Enrichment,” now abandoned; U.S. patent application Ser. No. 07/714,131, filed Jun. 10, 1991, entitled “Nucleic Acid Ligands,” now U.S. Pat. No. 5,475,096; U.S. patent application Ser. No. 07/931,473, filed Aug. 17, 1992, entitled “Methods for Identifying Nucleic Acid Ligands,” now U.S. Pat. No. 5,270,163 (see also WO 91/19813), each of which is herein specifically incorporated by reference in its entirety. Each of these applications, collectively referred to herein as the SELEX Patent Applications, describes a fundamentally novel method for making a Nucleic Acid Ligand to any desired Target molecule.
The SELEX method involves selection from a mixture of candidate oligonucleotides and step-wise iterations of binding, partitioning and amplification, using the same general selection scheme, to achieve virtually any desired criterion of binding affinity and selectivity. Starting from a mixture of Nucleic Acids, preferably comprising a segment of randomized sequence, the SELEX method includes steps of contacting the mixture with the Target under conditions favorable for binding, partitioning unbound Nucleic Acids from those Nucleic Acids which have bound specifically to Target molecules, dissociating the Nucleic Acid-Target complexes, amplifying the Nucleic Acids dissociated from the Nucleic Acid-Target complexes to yield a ligand-enriched mixture of Nucleic Acids, then reiterating the steps of binding, partitioning, dissociating and amplifying through as many cycles as desired to yield highly specific, high affinity Nucleic Acid Ligands to the Target molecule.
The basic SELEX method has been modified to achieve a number of specific objectives. For example, U.S. patent application Ser. No. 07/960,093, filed Oct. 14, 1992, entitled “Method for Selecting Nucleic Acids on the Basis of Structure,” now abandoned (see also U.S. Pat. No. 5,707,796), describes the use of the SELEX method in conjunction with gel electrophoresis to select Nucleic Acid molecules with specific structural characteristics, such as bent DNA. U.S. patent application Ser. No. 08/123,935, filed Sep. 17, 1993, entitled “Photoselection of Nucleic Acid Ligands,” now abandoned, (see also U.S. Pat. No. 5,763,177) describes a SELEX-based method for selecting Nucleic Acid Ligands containing photoreactive groups capable of binding and/or photocrosslinking to and/or photoinactivating a Target molecule. U.S. patent application Ser. No. 08/134,028, filed Oct. 7, 1993, entitled “High-Affinity Nucleic Acid Ligands That Discriminate Between Theophylline and Caffeine,” now abandoned (see also U.S. Pat. No. 5,580,737), describes a method for identifying highly specific Nucleic Acid Ligands able to discriminate between closely related molecules, termed Counter-SELEX. U.S. patent application Ser. No. 08/143,564, filed Oct. 25, 1993, entitled “Systematic Evolution of Ligands by EXponential Enrichment: Solution SELEX,” now abandoned, (see also U.S. Pat. No. 5,567,588) and U.S. patent application Ser. No. 08/792,075, filed Jan. 31, 1997, entitled “Flow Cell SELEX,” now U.S. Pat. No. 5,861,254, describe SELEX-based methods which achieve highly efficient partitioning between oligonucleotides having high and low affinity for a Target molecule. U.S. patent application Ser. No. 07/964,624, filed Oct. 21, 1992, entitled “Nucleic Acid Ligands to HIV-RT and HIV-1 Rev,” now U.S. Pat. No. 5,496,938, describes methods for obtaining improved Nucleic Acid Ligands after the SELEX process has been performed. U.S. patent application Ser. No. 08/400,440, filed Mar. 8, 1995, entitled “Systematic Evolution of Ligands by EXponential Enrichment: Chemi-SELEX,” now U.S. Pat. No. 5,705,337, describes methods for covalently linking a ligand to its Target.
The SELEX method encompasses the identification of high-affinity Nucleic Acid Ligands containing modified nucleotides conferring improved characteristics on the ligand, such as improved in vivo stability or improved delivery characteristics. Examples of such modifications include chemical substitutions at the ribose and/or phosphate and/or base positions. SELEX-identified Nucleic Acid Ligands containing modified nucleotides are described in U.S. patent application Ser. No. 08/117,991, filed Sep. 8, 1993, entitled “High Affinity Nucleic Acid Ligands Containing Modified Nucleotides,” now abandoned, (see also U.S. Pat. No. 5,660,985) that describes oligonucleotides containing nucleotide derivatives chemically modified at the 5- and 2′-positions of pyrimidines. U.S. patent application Ser. No. 08/134,028, now U.S. Pat. No. 5,580,737, supra, describes highly specific Nucleic Acid Ligands containing one or more nucleotides modified with 2′-amino (2′-NH2), 2′-fluoro (2′-F), and/or 2′-O-methyl (2′-OMe). U.S. patent application Ser. No. 08/264,029, filed Jun. 22, 1994, entitled “Novel Method of Preparation of Known and Novel 2′ Modified Nucleosides by Intramolecular Nucleophilic Displacement,” now abandoned, describes oligonucleotides containing various 2′-modified pyrimidines.
The SELEX method encompasses combining selected oligonucleotides with other selected oligonucleotides and non-oligonucleotide functional units as described in U.S. patent application Ser. No. 08/284,063, filed Aug. 2, 1994, entitled “Systematic Evolution of Ligands by Exponential Enrichment: Chimeric SELEX,” now U.S. Pat. No. 5,637,459 and U.S. patent application Ser. No. 08/234,997, filed Apr. 28, 1994, entitled “Systematic Evolution of Ligands by Exponential Enrichment: Blended SELEX,” now U.S. Pat. No. 5,683,867, respectively. These applications allow the combination of the broad array of shapes and other properties, and the efficient amplification and replication properties, of oligonucleotides with the desirable properties of other molecules. Each of the above described patent applications which describe modifications of the basic SELEX procedure are specifically incorporated by reference herein in their entirety.